Feedback control systems are generally utilized to stabilize the net output power level of associated lasers. Pulse width modulation control is generally utilized to control the duty cycle of the laser in order to obtain the desired net output power level.
Traditional CO2 laser feedback control systems uses partial reflectors mounted at 45 degrees with respect to the beam path. This beam sampling technique is polarization sensitive. Therefore, in most cases, a special optical coating is applied to overcome this sensitivity. Such optical coating narrows down the reflection bandwidth, making the reflector wavelength dependent. In practical cases, most standard grade, low cost, radio frequency (“RF”) driven CO2 lasers have their wavelength and polarization states randomly change. Accordingly, polarization and wavelength sensitive feedback control systems may generate inaccuracies, resulting in undesirable power fluctuations. Further, and as a result, it is often recommended to warm up these lasers prior to using them, such as for up to 30 minutes each time the laser is turned on, which makes them unsuitable for applications requiring low lasing time.
Another limitation of known feedback control systems is the presence of a second parasitic reflection happening on the second surface of the beam sampler. The two reflections can interfere at the detector causing an additional instability factor. To remedy this issue, it is often proposed to introduce an angle between the two reflective surfaces, which changes the direction of both reflected and transmitted beams.
Accordingly, improved laser feedback control systems are desired. In particular, laser feedback control systems which provide improved power stabilization control and are polarization insensitive would be advantageous.